1. Field of the Invention
The present invention relates to a backlight device and particularly to an edge light type backlight device for use in a liquid crystal display (LCD) or the like.
2. The Related Arts
An LCD device comprises, for example, a liquid crystal display panel and a backlight system mounted under the liquid crystal display panel for supplying light beams thereto. The backlight system mainly comprises a light source and a light guide plate, wherein the light guide plate is made of a transparent acrylic plastic plate and is used for guiding the light beams emitted by the light source to uniformly illuminate the liquid crystal display panel.
The light source emits light beams into the light guide plate, wherein the light beams are totally internally reflected. In order to diffuse the light beams and emit them uniformly from a top surface of the light guide plate, protrusions or recesses are located on a bottom surface of the light guide plate, or a plurality of light diffusion dot-patterns are formed on the bottom surface of the light guide plate.
Referring to FIG. 7 and FIG. 8, a conventional backlight system 9 comprises a plurality of light sources 40, which can be light emitting diodes, miniature bulbs, or other point sources, a cage 30 having a reflective coating thereon, a light guide plate 10, and a translucent sheet 20. The cage 30 has a plurality of locating grooves 31 therein. The light guide plate 10 comprises a light input surface 11 and a light output surface 12.
In assembly, the light sources 40 are arranged in the locating grooves 31 of the cage 30, and the light guide plate 10 is accommodated in the cage 30. The light input surface 11 of the light guide plate 10 is close to the light sources 40. The translucent sheet 20 is placed upon the light guide plate 10.
In operation, light beams emitted by the light sources 40 pass through the light input surface 11 and enter into the light guide plate 10, and then are transmitted out from the light output surface 12 of the light guide plate 10. After that, the light beams pass through the translucent sheet 20 to illuminate an LCD panel.
However, the light sources 40 have a certain emitting angle. For example, light emitting diodes used as the light sources 40 emit light beams with an emitting angle in a range of 30° to 130°. Referring to FIG. 8, because the light beams are refracted at the light input surface 11 when they pass there through, the emitting angle of the light beams is decreased. The largest emitting angle is about 119.653°. Therefore, the light guide plate 10 yields a plurality of dark areas 13, from which fewer light beams are emitted. Thus, the uniformity of emission from the light guide plate 10 is impaired.
It is desirable to provide an improved backlight system for use in a liquid crystal display, which overcomes the above problems.